I must say, most of the 1991-97 "2s" give me the creeps. Optics was the worst. Shadow made me tremble as well. Others include Blade and Paint. But the audio for Optics was just surreal.
Another one I've just thought of is the original Channel 4 ident, but instead of it forming up, it would be played backwards, so the blocks would eventually break away and leave the screen black, whilst the music was playing, when at that point you would normally expect no sound at all, except a Test Card tone or something.
Suffice to say I was never scared of idents when I was younger, although I used to have an fear of pylons (perhaps caused by one of the Play Safe PIFs!) so I was dreading the first time I saw the new Channel 4 "pylon" ident...
From the BBC2 idents the one I found scary was the rarely seen Crystal Ball ident. Also the original Channel 4 nightime idents from the late 80s were pretty scary and a coule of old Scottish idents were scary too like the original one with the spinning lion and the one from the 80s with the giant 'tiddlywinks' rolling about the screen.
Channel TV's logo from 1992 on TV Ark is truly scary. Not for the logo but the music. What the hell is that about? Like a primary school band warming up. Someone at Channel approved and paid for that!